@VictorJohnson: right-click in the plugins/insert/sends area in the mixer strip for the track, and select "New Insert". This will create a dialog that lets you connect the insert outputs to the audio interface outputs that the Eventide is connected to, and the insert inputs to the audio interface inputs that the Eventide is connected to.

For example, suppose your Eventide is stereo and connected to channels 3 and 4 of your audio interface. You would connect the insert outputs to system:playback_3 and system:playback_4, and the insert inputs to system:capture_3 and system:capture_4. Audio will flow through the insert, out through the audio interface to the Eventide, back to the audio interface and the insert and then continue through the mixer strip. Done.